Fabrication method of a polarizing grating

ABSTRACT

A fabrication method of a polarization grating is provided. The method includes providing a polarization-sensitive material; and causing two orthogonally polarized lights to scan the polarization-sensitive material and to meet on the polarization-sensitive material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the prioritybenefit of U.S. application Ser. No. 14/205,382, filed on Mar. 12, 2014,now allowed. The entirety of the above-mentioned patent application ishereby incorporated by reference herein and made a part of thisspecification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a display device and a fabricationmethod thereof and, in particular, to a projection device and afabrication method thereof.

2. Description of Related Art

In the area of display technology, when a large display frame isrequired, a flat panel display needs to have a commensurate size.However, a projection device with a smaller size can form a largedisplay frame on a screen. As a result, a projection device hasadvantage in the occasion where a number of people watch the displayframe together, such as conference, briefing or movie watching.Therefore, the projection device has an irreplaceable status in the areaof display technology.

In a conventional liquid-crystal-on-silicon (LCOS) projector, anunpolarized beam is polarized and then travels to an LCOS panel. TheLCOS panel reflects the polarized beam and modulates the polarizationstate of the polarized beam. A polarizing beam splitter then blocks partof the polarized beam having a polarization direction and traveling fromthe LCOS panel and allows another part of the polarized beam havinganother perpendicular polarization direction to travel to a projectionlens. When the unpolarized beam is polarized and passes through thepolarizing beam splitter, the optical efficiency of the LCOS projectoris considerably reduced. For a conventional color filter LCOS projector,its optical efficiency is about 3-4%.

SUMMARY OF THE INVENTION

Accordingly, the invention is directed to a projection device, which hashigher optical efficiency.

The invention is directed to a fabrication method of a polarizationgrating, which can fabricate a polarization grating with good quality.

According to an embodiment of the invention, a projection deviceincluding a light source, a reflective spatial polarization modulator, apolarization grating, and a projection lens is provided. The lightsource is configured to provide a light beam. The reflective spatialpolarization modulator is disposed on a path of the light beam andconfigured to reflect the light beam and modulate a polarization stateof the light beam. The polarization grating is disposed on the path ofthe light beam between the light source and the reflective spatialpolarization modulator, wherein the reflective spatial polarizationmodulator reflects the light beam from the reflective spatialpolarization modulator back to the polarization grating. The projectionlens is disposed on the path of the light beam from the reflectivespatial polarization modulator, wherein the polarization grating isdisposed on the path of the light beam between the reflective spatialpolarization modulator and the projection lens.

According to an embodiment of the invention, a fabrication method of apolarization grating is provided. The method includes providing apolarization-sensitive material; and causing two orthogonally polarizedlights to scan the polarization-sensitive material and to meet on thepolarization-sensitive material.

In view of the above, the projection device according to the embodimentof the invention adopts the polarization grating to diffract the lightbeam from the light source, and the light energy transferred to theprojection lens can be concentrated on the light beam with a certaindiffracted order. As a result, the optical efficiency of the projectiondevice is good, so that the projection device can provide an image framewith high brightness. In addition, in the fabrication method of thepolarization grating, the polarization-sensitive material is processedby light but not by contacting the polarization-sensitive material withalignment layers. Consequently, the contact problem with the alignmentlayers can be prevented. Therefore, the fabrication method of thepolarization grating is simple and can fabricate a polarization gratingwith good quality.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1A is a schematic view of a projection device according to anembodiment of the invention.

FIG. 1B is a schematic cross-sectional view of the reflective spatialpolarization modulator in FIG. 1A.

FIG. 1C is the schematic top view of the polarization grating in FIG.1A.

FIG. 2 is a schematic top view of a polarization grating according toanother embodiment of the invention.

FIG. 3 is a schematic view of a projection device according to anotherembodiment of the invention.

FIG. 4A is a schematic view illustrating a fabrication method of apolarization grating.

FIG. 4B is a schematic diagram showing the coordinate and the positionof the lights in FIG. 4A irradiating the polarization-sensitive materialin FIG. 4A.

FIG. 4C is a schematic diagram showing the combined polarization stateof the two lights of FIG. 4A when the two lights meet on thepolarization-sensitive material in FIG. 4A.

FIG. 5A and 5B are respectively other variations of FIGS. 4B and 4C inanother embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

FIG. 1A is a schematic view of a projection device according to anembodiment of the invention, FIG. 1B is a schematic cross-sectional viewof the reflective spatial polarization modulator in FIG. 1A, and FIG. 1Cis the schematic top view of the polarization grating in FIG. 1A.Referring to FIGS. 1A to 1C, the projection device 100 in thisembodiment includes a light source 110, a reflective spatialpolarization modulator 120, a polarization grating 130, and a projectionlens 140 is provided. The light source 110 is configured to provide alight beam 112. In this embodiment, the light beam 112 is a white beam,and the light source 110 includes at least one white light-emittingdiode (LED) emitting the white beam. However, in other embodiments, thelight source 110 may be an ultra-high-pressure (UHP) lamp emitting awhite beam. Alternatively, the light beam 112 may include a plurality ofsub-beams of different colors, and the different colors mix to formwhite. For example, the light beam 112 may include red, green, and bluesub-beams, and the three sub-beams mix to form a white beam. Moreover,the light source 110 may include a plurality of LEDs of differentcolors, and the sub-beams of different colors may be emitted from LEDsof different colors, respectively. In one embodiment, the sub-beams ofdifferent colors are simultaneously emitted from the light source 110.However, in another embodiment, the sub-beams of different colors areemitted from the light source 110 by turns. In another embodiment, thelight source 110 may include at least one laser emitter, for example, atleast one laser diode.

The reflective spatial polarization modulator 120 is disposed on a pathof the light beam 112 and configured to reflect the light beam 112 andmodulate a polarization state of the light beam 112. The reflectivespatial polarization modulator 120 may be a liquid-crystal-on-silicon(LCOS) panel. In this embodiment, the reflective spatial polarizationmodulator 120 is a color filter LCOS panel. Specifically, in thisembodiment, the color filter LCOS panel includes a silicon substrate210, a plurality of pixel electrodes 222, an insulation layer 230, analignment layer 240, a liquid crystal layer 250, an alignment layer 260,a transparent conductive layer 270, a color filter array 280, and atransparent substrate 290. A plurality of transistors 212 are arrangedon the silicon substrate 210 in an array. The transistors 212 may beelectrically coupled to a plurality of scan lines and a plurality ofdata lines on the silicon substrate 210. The pixel electrodes 222 areelectrically coupled to and cover the transistors 212, respectively. Thepixel electrodes 222 are made of metal, for example, aluminum. Theinsulation layer 230 separates the pixel electrodes 222. The alignmentlayer 240 covers the pixel electrodes 222. The color filter array 280 isdisposed on the transparent substrate 290. The transparent substrate 290may be made of glass or any other appropriate transparent material. Thecolor filter array 280 includes a plurality of color filters withdifferent colors. For example, the color filter array 280 includes aplurality of red filters 282, a plurality of green filters 284, and aplurality of blue filters 286 arranged in an array. The transparentconductive layer 270 covers the color filter array 280, and thealignment layer 260 covers the transparent conductive layer 270. Thetransparent conductive layer 270 is, for example, made of indium tinoxide (ITO). The liquid crystal layer 250 is filled between thealignment layer 240 and the alignment layer 260.

In this embodiment, the color filter array 280 is disposed between thealignment layer 260 and the transparent substrate 290, but the inventionis not limited thereto. In other embodiments, the color filter array 280is disposed between the pixel electrodes 222 and the alignment layer 240or may be disposed at any other appropriate position.

In another embodiment, the color filter array 280 may not be adopted;that is, there is no color filter array 280 between the transparentconductive layer 270 and the transparent substrate 290.

The polarization grating 130 is disposed on the path of the light beam112 between the light source 110 and the reflective spatial polarizationmodulator 120, and the reflective spatial polarization modulator 120reflects the light beam 112 from the reflective spatial polarizationmodulator 120 back to the polarization grating 130. The projection lens140 is disposed on the path of the light beam 112 from the reflectivespatial polarization modulator 120, and the polarization grating 130 isdisposed on the path of the light beam 112 between the reflectivespatial polarization modulator 120 and the projection lens 140. Thelight beam 112 from the polarization grating 130 passes through thetransparent substrate 290, the color filter array 280, the transparentconductive layer 270, the alignment layer 260, the liquid crystal layer250, and the alignment layer 240 in sequence to reach the pixelelectrodes 222. The light beam 122 is then reflected by the pixelelectrode 222 and then passes through the alignment layer 240, theliquid crystal layer 250, the alignment layer 260, the transparentconductive layer 270, the color filter array 280, and the transparentsubstrate 290 in sequence to reach the projection lens 140.

In this embodiment, the polarization grating 130 includes a plurality offirst phase retardation strips 132 and a plurality of second phaseretardation strips 134 arranged alternately in a first direction D1.Each of the first phase retardation strips 132 extends along a seconddirection D2, and each of the second phase retardation strips 134extends along the second direction D2. In this embodiment, the firstdirection D1 and the second direction D2 are perpendicular a thirddirection D3, the third direction D3 is parallel to the normal of thepolarization grating 130, and the first direction D1 is perpendicular tothe second direction D2. The slow axis 131 of the first phaseretardation strips 132 is perpendicular to the slow axis 133 of thesecond phase retardation strips 134. The slow axes 131 and 133 of thefirst phase retardation strips 132 and the second phase retardationstrips 134 may be the extraordinary axes of the first phase retardationstrips 132 and the second phase retardation strips 134, or may be theordinary axes of the first phase retardation strips 132 and the secondphase retardation strips 134. In this embodiment, the first phaseretardation strips 132 and the second retardation strips 134 areperiodically arranged along the first direction Dl.

In this embodiment, the light beam 112 emitted from the light source 110before traveling to the polarization grating 130 is an unpolarized beam.The polarization grating 130 is diffracted by the polarization grating130 mainly into a +1^(st) diffracted order sub-beam and a −1^(st)diffracted order sub-beam. When the polarization grating 130 iswell-designed, the intensity of the 0^(th) diffracted order sub-beam ismuch less than that of the +1^(st) diffracted order sub-beam and muchless than that of the −1^(st) diffracted order sub-beam. Therefore, the0^(th) diffracted order sub-beam can be neglected.

The case in which the light beam 112 is normally incident on thepolarization grating 130 is first described as follows. The +1stdiffracted order sub-beam may be clockwise circularly polarized sub-beamand have a diffracted angle of +θ with respect to the normal of thepolarization grating 130. The −1st diffracted order sub-beam may becounter-clockwise circularly polarized sub-beam and have a diffractedangle of −θ with respect to the normal of the polarization grating 130.When any pixel of the reflective spatial polarization modulator 120 isin a state like a mirror plus a transparent layer, i.e. a 0 wavelengthretarder, the +1st diffracted order sub-beam is reflected by the pixelalong a direction inclined with respect to the normal of thepolarization grating 130 by the angle of +θ and maintains the clockwisecircular polarization. Next, the +1st diffracted order sub-beam isdiffracted by the polarization grating 130 along a direction inclinedwith respected to the normal of the polarization grating 130 by an angleof +2θ and maintains the clockwise circular polarization, and is called“first side diffraction sub-beam S1” hereinafter. Moreover, the −1stdiffracted order sub-beam is reflected by the pixel along a directioninclined with respect to the normal of the polarization grating 130 bythe angle of −θ and maintains the counter-clockwise circularpolarization. Next, the −1st diffracted order sub-beam is diffracted bythe polarization grating 130 along a direction inclined with respectedto the normal of the polarization grating 130 by an angle of −2θ andmaintains the counter-clockwise circular polarization, and is called“second side diffraction sub-beam S2 hereinafter”. On the other hand,when any pixel of the reflective spatial polarization modulator 120 isin a state like a mirror plus a quarter wave plate, the +1st diffractedorder sub-beam is reflected by the pixel along a direction inclined withrespect to the normal of the polarization grating 130 by the angle of +θand has a polarization state changed to the counter-clockwise circularpolarization, and the −1st diffracted order sub-beam is reflected by thepixel along a direction inclined with respect to the normal of thepolarization grating 130 by the angle of −θ and has a polarization statechanged to the clockwise circular polarization. Next, the +1stdiffracted order sub-beam and the −1st diffracted order sub-beam arediffracted by the polarization grating 130 along the normal of thepolarization, and are combined into a central diffraction sub-beam SC.

In this embodiment, the light beam 112 is obliquely incident on thepolarization grating 130, so that the first side diffraction sub-beamS1, the second side diffraction sub-beam S2, and the central diffractionsub-beam SC are respectively inclined with respect to those in the abovecase. Moreover, in this embodiment, the central diffraction sub-beam SCserves as an image beam and enters the projection lens 140, but thefirst side diffraction sub-beam S1 and the second side diffractionsub-beam S2 does not travels to the projection lens 140. The projectionlens 140 projects the central diffraction sub-beam SC, i.e. the imagebeam, onto a screen to form an image frame on the screen.

In this embodiment, the projection device 100 further includes a totalinternal reflection (TIR) prism 150 disposed on the path of the lightbeam 112 between the light source 110 and the polarization grating 130and on the path of the light beam 112 between the polarization grating130 and the projection lens 140. The TIR prism 150 may include twoprisms 152 and 154. The prism 152 leans against the prism 154 and has atotal internal reflection surface (TIR surface) 156 facing the prism154. The TR surface 156 totally reflects the light beam 112 from thelight source 110 to the polarization grating 130, and allows the centraldiffraction sub-beam SC to pass through and then to travel to theprojection lens 140. In this embodiment, the projection device 100 mayfurther includes at least one lens 170 disposed on the path of the lightbeam 112 between the prism 152 and the light source 110 to condense thelight beam 112.

In this embodiment, the projection device 100 further includes a lightshield 160 disposed on the path of the light beam 112 reflected from thereflective spatial polarization modulator 120 and diffracted by thepolarization grating 130. The light shield 160 is configured to blockthe diffracted light beam 112 with part of diffracted orders (e.g. thefirst and second side diffraction sub-beams 51 and S2) from traveling tothe projection lens 140 and allow the diffracted light beam 112 withanother part of diffracted orders (e.g. the central diffraction sub-beamSC) to travel to the projection lens 140.

In another embodiment, the light shield 160 may not be adopted, and theprojection lens 140 has an aperture stop with a smaller aperturediameter, so that the central diffraction sub-beam SC can pass throughthe projection lens 140, but the side diffraction sub-beams S1 and S2cannot. Alternatively, in another embodiment, the side diffractionsub-beam S1 may be totally reflected by the TIR surface 156 and thuscannot travel to the projection lens 140, and the included angle betweenthe side diffraction sub-beam S2 and the normal of the polarizationgrating 130 is large enough so that the side diffraction sub-beamdeviates from the projection lens 140.

The projection device 100 in this embodiment adopts the polarizationgrating 130 to diffract the light beam 112 from the light source 110,and the light energy transferred to the projection lens 140 can beconcentrated on the light beam 112 with a certain diffracted order (e.g.the central diffraction sub-beam). As a result, a polarizing beamsplitter (PBS), which reduces the optical efficiency, can be notadopted. Therefore, the optical efficiency of the projection device 100is good, so that the projection device 100 can provide an image framewith high brightness.

FIG. 2 is a schematic top view of a polarization grating according toanother embodiment of the invention. Referring to FIG. 2, thepolarization grating 130 a in this embodiment may replace thepolarization grating 130 in FIG. 1A to form another embodiment of theprojection device. In this embodiment, the polarization grating 130 hasa slow axis 135 a rotationally varied along the first direction D1periodically and not varied along the second direction D2.

FIG. 3 is a schematic view of a projection device according to anotherembodiment of the invention. Referring to FIG. 3, the projection device100 b in this embodiment is similar to the projection device 100 in FIG.1A, and the difference therebetween is as follows. In the projectiondevice 100 b, a reflector 150 c is adopted to replace the TIR prism 150.The reflector 150 c is disposed on the path of the light beam 112between the light source 110 and the polarization grating 130. Thereflector 150 c blocks the diffracted light beam 112 with part ofdiffracted orders (e.g. the central diffraction sub-beam SC) fromtraveling to the projection lens 140. In this embodiment, the reflector150 c reflects the central diffraction sub-beam SC, so as to cause thecentral diffraction sub-beam SC not to travel to the projection lens140. Moreover, the reflector 150 c allows the diffracted light beam 112with another part of diffracted orders (e.g. the first and second sidediffraction sub-beams 112 and 114) to travel to the projection lens 140.This is because the first and second side diffraction sub-beams 112 and114 from the polarization grating 130 does not blocked by the reflector150 c. In this embodiment, the reflector 150 c is a mirror. However, inother embodiments, the reflector 150 c may be a reflective prism. Then,the first and second side diffraction sub-beams 112 and 114 areprojected onto a screen 105.

FIG. 4A is a schematic view illustrating a fabrication method of apolarization grating, FIG. 4B is a schematic diagram showing thecoordinate and the position of the lights in FIG. 4A irradiating thepolarization-sensitive material in FIG. 4A, and FIG. 4C is a schematicdiagram showing the combined polarization state of the two lights ofFIG. 4A when the two lights meet on the polarization-sensitive materialin FIG. 4A. Referring to FIGS. 4A to 4C, the fabrication method of thepolarization grating in this embodiment may be used to fabricate theabove polarization grating 130. The fabrication method includesproviding a polarization-sensitive material 50. In this embodiment, thepolarization-sensitive material 50 is a liquid crystal material. Then,the fabrication method includes causing two orthogonally polarizedlights 62 and 64 to scan the polarization-sensitive material 50 and tomeet on the polarization-sensitive material 50.

In this embodiment, the fabrication method further includes emitting anoriginal light 60 and splitting the original light 60 into the twoorthogonally polarized lights 62 and 64. The original light 60 is, forexample, a laser light. In this embodiment, a laser source 70 may beused to emit the original light 60. Moreover, in this embodiment, apolarizing beam splitter (PBS) 80 is disposed on the path of theoriginal light 60 to split the original light 60 into two orthogonallypolarized lights 62 and 64. In this embodiment, the original light 60,the light 62 and the light 64 are linearly polarized lights. Thepolarization direction P1 of the light 62 is perpendicular to thepolarization direction P2 of the light 64. The polarization direction P0of the original light 60 and the polarization direction P1 of the light62 form an included angle of 45°. The polarization direction P0 of theoriginal light 60 and the polarization direction P2 of the light 64 forman included angle of 45°. Two scanning mirrors 92 and 94 are adopted torespectively reflect the two lights 62 and 64, so as to cause the twolights 62 and 64 to meet on the polarization-sensitive material 50. Inthis embodiment, an included angle cp is formed between the twoorthogonally polarized lights 62 and 64 and at an incident position L ofthe two orthogonally polarized lights 62 and 64 incident on thepolarization-sensitive material 50.

When the two scanning mirrors 62 and 64 rotate, the two lights 62 and 64scan the polarization-sensitive material 50 along a direction, forexample the x direction. At this time, the difference of the opticalpath length between the two lights 62 and 64 is changed, so that thecombined polarization state of the two lights 62 and 64 on thepolarization-sensitive material 50 is changed. In FIG. 4C, the combinedpolarization state of the two lights 62 and 64 is varied along the xdirection. The extraordinary axis of the liquid crystal molecules of thepolarization-sensitive material 50 is rotated to an orientationperpendicular to the combined polarization direction. As a result, theslow axis of the polarization-sensitive material 50 is periodicallychanged along the x direction but not changed along the y direction.After the two lights 62 and 64 scan the polarization-sensitive material50, the polarization-sensitive material 50 is cured to form thepolarization grating 130 in FIG. 1C, wherein the x direction in FIG. 4Acorresponds to the first direction D1 in FIG. 1C, the y direction inFIG. 4A corresponds to the second direction D2 in FIG. 1C, and the zdirection is perpendicular to the x direction and the y direction. InFIG. 4C, there are a circular polarization state and ellipticpolarization state between two adjacent orthogonal linear polarizationstates, so that the boundary between the adjacent first and second phaseretardation strips 132 and 134 is blurry in fact.

In another embodiment, referring to FIGS. 5A and 5B two quarter waveplates may be respectively disposed on the paths of the lights 92 and 94between the PBS 80 and the polarization-sensitive material 50, so thattwo orthogonally circularly polarized lights meet on thepolarization-sensitive material 50. For example, the lights 92 isconverted into a counter-clockwise circularly polarized light beforereaching the polarization-sensitive material 50, and the lights 94 isconverted into a clockwise circularly polarized light before reachingthe polarization-sensitive material 50. In this case, when the lights 92and 94 scan the polarization-sensitive material 50, the combinedpolarization state of the lights 92 and 94 is always linear, and thelinear polarization direction of the combined polarization state isrotationally varied along the x direction periodically and not variedalong the y direction. As a result, after the polarization-sensitivematerial 50 is scanned and cured, the polarization grating 130 a isformed. In still another embodiment, the lights 92 and 94 may be twoorthogonal elliptically polarized lights.

In the fabrication method of the polarization grating in thisembodiment, the polarization-sensitive material 50 is processed by lightbut not by contacting the polarization-sensitive material with alignmentlayers. Consequently, the contact problem (e.g. contamination) with thealignment layers can be prevented. Therefore, the fabrication method ofthe polarization grating is simple and can fabricate a polarizationgrating with good quality. Moreover, the optical path lengths of thelights 62 and 64 are easy to adjust, so that the spatial period of thepolarization grating may be freely designed. Furthermore, the spatialperiod of the polarization grating may be smaller than the spatialperiod which the conventional photolithography can achieve. That is tosay, the fabrication method of the polarization grating can fabricate apolarization grating with a smaller spatial period.

In conclusion, the projection device according to the embodiment of theinvention adopts the polarization grating to diffract the light beamfrom the light source, and the light energy transferred to theprojection lens can be concentrated on the light beam with a certaindiffracted order. As a result, the optical efficiency of the projectiondevice is good, so that the projection device can provide an image framewith high brightness. In addition, in the fabrication method of thepolarization grating, the polarization-sensitive material is processedby light but not by contacting the polarization-sensitive material withalignment layers. Consequently, the contact problem with the alignmentlayers can be prevented. Therefore, the fabrication method of thepolarization grating is simple and can fabricate a polarization gratingwith good quality.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of theinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the invention covermodifications and variations of this invention provided they fall withinthe scope of the following claims and their equivalents.

What is claimed is:
 1. A fabrication method of a polarization gratingcomprising: providing a polarization-sensitive material; providing twoorthogonally polarized lights; and causing the two orthogonallypolarized lights to be reflected by two scanning mirrors respectivelytoward an incident position of the polarization-sensitive material andto scan the polarization-sensitive material along a direction, so as toform the polarization grating, wherein the incident position is aconvergence point of the two orthogonally polarized light on a surfaceof the polarization-sensitive material.
 2. The fabrication method of thepolarization grating according to claim 1, wherein the two orthogonallypolarized lights meet on the incident position of thepolarization-sensitive material, and an included angle is formed betweenthe two orthogonally polarized lights at the incident position.
 3. Thefabrication method of the polarization grating according to claim 1further comprising: emitting an original light; and splitting theoriginal light into the two orthogonally polarized lights.
 4. Thefabrication method of the polarization grating according to claim 3,wherein the original light is a laser light.
 5. The fabrication methodof the polarization grating according to claim 3, wherein the method ofsplitting the original light into the two orthogonally polarized lightscomprises disposing a polarizing beam splitter on a path of the originallight to split the original light into the two orthogonally polarizedlights.
 6. The fabrication method of the polarization grating accordingto claim 1, wherein the polarization-sensitive material is a liquidcrystal material.
 7. The fabrication method of the polarization gratingaccording to claim 1 further comprising: converting the two orthogonallypolarized light to orthogonally circularly polarized light.
 8. Thefabrication method of the polarization grating according to claim 7,wherein the method of converting the two orthogonally polarized light toorthogonally circularly polarized light comprises disposing two quarterwave plates along a path of the two orthogonally polarized lightrespectively and between the polarizing beam splitter and thepolarization-sensitive material.